Engine systems may be configured with boosting devices, such as turbochargers or superchargers, for providing a boosted aircharge and improving peak power outputs. The use of a compressor allows an engine with smaller displacement to provide as much power as a larger displacement engine, but with additional fuel economy benefits. However, compressors are prone to surge. For example, when an operator tips-out of an accelerator pedal, an engine intake throttle closes, leading to reduced forward flow through the compressor, and a potential for surge. Surge can lead to noise, vibration, and harshness (NVH) issues such as undesirable noise from the engine intake system. In extreme cases, surge may result in compressor damage. To address compressor surge, engine systems may include a compressor recirculation valve (CRV) coupled across the compressor to enable rapid decaying of boost pressure. The CRV may recirculate compressed air from the compressor outlet to the compressor inlet allowing a decrease in pressure at the compressor outlet.
The CRV may comprise a throttle and a position sensor for indicating a change in a position of the throttle of the CRV. Degradation of the CRV may be diagnosed when the position sensor does not register a change in the position of the throttle in response to a command to alter throttle position. For example, the throttle of the CRV may be stuck at a given position. Another example approach to diagnose degradation of the CRV is shown by Wegener et al. in U.S. Pat. No. 7,926,335. Herein, changes in charging pressure in response to a triggering of the CRV are analyzed. Specifically, the CRV may be diagnosed to be stuck in a mostly open position if the charging pressure downstream of an intake compressor does not increase as expected when the CRV is triggered to a closed position.
The inventors herein have identified potential issues with the above approaches. As an example, degradation of the CRV may be due to degradation in a specific component of the CRV. For example, the throttle of the CRV may be stuck and/or the position sensor of the CRV may be degraded. Thus, an indication of degradation based on the position sensor not registering a change in position may be for the CRV as a whole and may not identify specific component degradation. Further, by monitoring changes in charging pressure as shown in U.S. Pat. No. 7,926,335, degradation of the CRV throttle may be detected whereas degradation of the position sensor of the CRV may not be specifically diagnosed. As such, U.S. Pat. No. 7,926,335 primarily detects a CRV that is stuck in an open or mostly open position.
In one example, some of the above issues may be addressed by a method for a boosted engine, comprising differentiating between degradation of a throttle of a compressor recirculation valve (CRV) and a position sensor of the CRV based on each of a throttle inlet pressure and commanded position of the throttle of the CRV. Accordingly, component specific degradation may be identified.
For example, an engine system may include a compressor having a compressor recirculation passage coupling an outlet of the compressor to the compressor inlet. In alternate embodiments, the recirculation path may couple an outlet of a charge air cooler to the compressor inlet. Flow through the recirculation path may be controlled via a compressor recirculation valve (CRV). The CRV may be a continuously variable compressor recirculation valve (CCRV). An engine controller may be configured to adjust a position of the CRV based on changes in airflow through an intake throttle so as to reduce compressor surge. Further, the engine controller may receive signals from a position sensor of the CRV confirming the adjusted position of the CRV, particularly the throttle of the CRV. Additionally, a throttle inlet pressure sensor located upstream of the intake throttle and downstream of the compressor may communicate changes in throttle inlet pressure (TIP) to the controller. The controller may, thus, command a change in position of the CRV, receive feedback from the position sensor of the CRV to confirm the change in position, and receive indication of resulting changes in TIP from the TIP sensor. If the position sensor indicates a lack of change in the position of the CRV in response to the commanded change in position, yet an expected change in TIP is observed, the position sensor may be diagnosed to be degraded. Alternatively, if the position sensor indicates a lack of change in the position of the CRV in response to the commanded change in position, and the expected change in TIP is not observed, the throttle of the CRV may be diagnosed to be degraded.
In this way, a distinction between degradation of the CRV throttle and degradation of the CRV position sensor may be accomplished. By identifying the specific component of the CRV that is degraded, a more accurate remedial action may be taken. As such, cost of repair may also be reduced by identifying the specific degraded component in the CRV. Further, ascertaining specific component degradation may be easily achieved by simply monitoring TIP and the output of the position sensor in the CRV in response to a command to the CRV by the controller. Thus, additional sensors may not be required. Overall, a more accurate determination of degradation in the CRV may be achieved without an increase in expenses.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.